1. Field of the Invention
The present invention relates to a device and a method for separating semiconductor devices formed on a wafer, and more particularly to separating a wafer into individual semiconductor chips without using wafer sawing tape.
2. Description of the Related Arts
After fabrication of integrated circuits a semiconductor wafer, a sawing process separates the semiconductor wafer into individual semiconductor integrated circuit devices for packaging. FIG. 1 is a flowchart depicting a conventional semiconductor packaging process 10. Semiconductor packaging process 10 begins with sawing a semiconductor wafer to separate the wafer into individual semiconductor devices or chips. Before sawing, a wafer sawing tape is typically attached to the back surface of the wafer. The wafer sawing tape keeps the chips together after the sawing. After the sawing, each of the chips is removed from the tape and attached on a die pad of a lead frame. Then, wirebonding connects bonding pads of a chip to respective inner leads of the lead frame with Au or Al wires. Finally, an encapsulant such as an epoxy molding compound encapsulates the semiconductor chip, the wires, and the inner leads and protects the semiconductor chip from the external environment.
FIGS. 2 to 4 illustrate the sawing of a wafer. In particular, FIG. 2 shows a semiconductor wafer 12 attached to a wafer tape 11, and FIGS. 3 and 4 are cross-sectional views taken along the line III--III of FIG. 2 respectively before and after sawing. Wafer mounting for sawing attaches wafer tape 11 to the backside (the side without integrated circuit patterns) of semiconductor wafer 12 and a wafer ring 13 to wafer tape 11 on the same side as semiconductor wafer 12. Wafer ring 13 facilitates handling of wafer 12. Wafer tape 11 is typically a 80 .mu.m to 120 .mu.m thick PVC (Polyvinyl Chloride) or UV (Ultraviolet) sensitive tape, and the inner diameter of wafer ring 13 is greater than the diameter of wafer 12. After the wafer mounting, wafer 12 is transferred to a wafer sawing (or cutting) apparatus as mounted on tape 11 and supported by wafer ring 13.
In sawing wafer 12, a rotating diamond blade moves along scribe lines 14, which are between the semiconductor devices. The blade cuts through 90% to 100% of the thickness of wafer 12. In the case of the 100% cutting, the blade may partially cut wafer tape 11. After sawing wafer 12, the separate semiconductor chips 16 (FIG. 4) remain attached to tape 11.
A die attaching apparatus picks up each semiconductor chip 16 from wafer tape 11 and bonds the semiconductor chip 16 to a lead frame. However, a fragment of the adhesive from wafer tape 11 may remain on the back surface of semiconductor chip 16. The remaining adhesive can cause defects in device packaging, particularly in LOC (Lead-On-Chip) packages. For example, the adhesive fragment can cause delamination between the back surface of semiconductor chip 16 and the encapsulant that contacts the back surface. The delamination sometimes causes package cracking, which is one of the most serious problems of plastic packages.